Polyurethane is an example of a polymer which is synthesized by condensation reaction of fluid monomers in a vessel. During the reaction process, different molecular groups react with each other to chemically link, and they in turn link with other monomers to form even larger molecules. Once the original reactants have been mixed, the on-going reaction continues to have fluidity until the reaction concludes with a sudden transformation of the mixture into a solid of high molecular weight.
In the practice of dentistry, which includes general dentistry and related specialties, the above-described process is used to fabricate certain dental devices and dental aids. For example, an impression of a person's dental arch can provide a cavity into which an on-going reaction of reactants is introduced. When the reaction concludes, the result is a solid polymeric model of the person's dental arch which when removed from the impression can be used as needed.
Preparation of a mixture of reactants requires care in accurately measuring the quantity of each reactant to be used. Failure to measure the proper quantity of each reactant may result in an imperfect finished product which cannot be used and becomes waste because the process is not reversible.
A further factor in the process is length of time available before a reaction concludes. Because the reaction commences with mixing of the reactants, a limited time exists until the reaction concludes. A person preparing a mixture of monomers first performs their mixing in a vessel and once the reactants have been sufficiently mixed, pours the mixture into a form such as an arch impression. Failure to complete the pour before the mixture solidifies will not produce the desired result. Furthermore, if air bubbles are present in the pour, sufficient time to puncture them before solidification of the mixture may not be available.